The present invention refers to a rotary feeder for granulated bulk material.
German Patent No. DE 34 45 710 C2 describes a rotary feeder of the type having a housing with a supply well ending in an inlet area with a pre-stripping edge extending along a section which is passed last by the rotor blades in rotational direction of the rotor. The pre-stripping edge runs about one to two grain diameters above the generated cylindrical surface defined by the rotating radially outer end faces of the rotor blades and is followed by a stripping edge which runs at the inner wall of the housing. In plan view, the stripping edge is V-shaped, with its tip pointing in rotating direction of the rotor, and includes two sections extending symmetrically to the plane of symmetry which is oriented perpendicular to the rotor shaft. Each section extends from a side cover of the housing to the tip which lies in the afore-mentioned plane of symmetry so that the sections of the stripping edge bound a pocket-like recess at the inner wall of the housing, with each section describing with the generatrix of the generated cylindrical surface defined by the radial end faces of the rotor blades an angle which corresponds at least to the angle of repose between the bulk material and the rotor material.
The particular constructive design of this prior art prevents grains of bulk material from being sheared off between the leading edges of the end faces of the rotor blades and the first housing edge passed by the blades. Jammed or sheared off grains of bulk material cause not only an overall power increase but also a characteristic hacking noise of the rotor as well as increased wear. In addition to the afore-mentioned pre-stripping edge and V-shaped stripping edge, the rotary feeder according to the DE 34 45 710 C2 requires the provision of a deflector or displacement body which is situated within the supply well. The deflector is dimensioned such that beneath the deflector the bulk material forms a sloped cavity which at least is equal to the volume of bulk material stripped by the stripping edge in direction to this sloped cavity. The use of such a deflector is disadvantageous as it necessarily obstructs the supply of bulk material in the supply well.
Without arrangement of such a deflector, other constructive means must be provided to ensure that at nominal speed of the rotor the amount of bulk material fed through the supply well is smaller than the volume of the compartment moving past the supply well Thus, the compartments are only partly filled in order to provide sufficient space for receiving granulates stripped off by the stripping edge. Hence, the metering volume cannot fully be utilized.